1. Field of the Invention
This invention relates to a method and system for assisting the high throughput use of computer-aided detection systems. One primary aspect of high throughput processing relates to automated detection and handling of errors in the film digitization process.
2. Discussion of Related Prior Art
In 2001 an estimated 239,300 women were diagnosed with breast cancer and 40,200 women died from it. Mammography, along with physical examination, is the current procedure of choice for breast cancer screening. Screening mammography has been responsible for an estimated 30 to 35 percent reduction in breast cancer mortality rates. Although mammography is the preferred means of breast cancer screening, it is not perfect. Ten to thirty percent of women diagnosed with breast cancer have their mammograms interpreted as negative. Furthermore, of the malignancies missed by radiologists, an estimated two-thirds are retrospectively evident in the screening mammograms. Missed detections may be attributed to several factors including: poor image quality, interpretation error, lesion obscuration, subtle nature of radiographic findings, eye fatigue, or oversight.
To increase sensitivity, a double reading has been suggested. However, the additional time and expense of a second radiologist makes this option unlikely. Alternatively, a computer-aided diagnosis system may act as a “second reader” to assist the radiologist in detecting and diagnosing lesions. Computer-aided second reading systems, such as the commercially available Second Look® CAD system, (CADx Systems, Beavercreek, Ohio) have been clinically proven to decrease the rate of missed cancers. Thus, the computer-aided second reading clearly benefits women and their families.
The promise of earlier detection has made many women choose centers providing CAD services. The U.S. government encourages the purchase and use of CAD systems by providing reimbursement to radiologists or hospitals using such systems. In the four and a half years of commercial availability, approximately 5 million women have had their mammograms processed by CAD systems. As the number of cases continues to increase, automated methods for efficient processing and billing for CAD services are essential.
An overview of the typical workflow a mammography center is now provided. A radiology technologist enters patient identification information into an electronic system. Then, the technologist positions the patient in the mammography x-ray device and exposes four films, collectively referred to as a case. The films include two views of each breast, the cranio-caudal and medial-lateral oblique. Before development, patient information may be “flashed” onto the films. They are then developed and inspected to ensure compliance with the Mammographic Quality Standards Act (MQSA). MQSA compliant cases are then loaded into the digitizer of the CAD system by the radiology technician. The technologist uses interface devices such as a keyboard, mouse, touch screen, or speech recognition application to control the CAD system operation and input patient identification information. The digitizer feeds the films one at a time, creating a set of four digital images from a typical case. These digital images are analyzed for signs of cancer by algorithms in the CAD system.
The CAD system produces a visual or textual indication of the location and type of cancer indicator suspected. The output is typically either a printed page or electronic file consisting of the digital mammogram images with suspicious regions highlighted by markers; different marker styles are used to denote different indicators of cancer. When the CAD output is a printed page, it may be stored with the films. When the CAD output is an electronic file, it is stored and recorded such that it may be recalled from patient identification information and printed or displayed on a monitor. The radiologist subsequently uses the CAD output during an interpretation phase. The procedure for incorporating CAD system outputs is given in U.S. Pat. No. 6,115,488, herein incorporated by reference.
To maximize technologist productivity and efficiency, it is desirable to accumulate a number of cases before processing. Typically, the number of accumulated cases requires an overnight's amount of time to process. The collection of films is loaded into the digitizer, patient information is entered, and commands issued to the CAD system to begin processing in the “batch” mode. The cases are processed overnight, producing a collection of CAD outputs. The next morning, the processing is complete. Currently, the average time required to process a standard four-film case is approximately 4-6 minutes. Assuming 14 hours available in an overnight interval, 210 to 140 cases may be processed in an otherwise unused time span. For systems creating paper output, the pages are associated with the proper films for subsequent use by a radiologist.
Batch operation has the disadvantage of being dependent on perfect feeding of films through the digitizer. A common feed error in digitizers is the “double feed” where two films are pulled through the system as one. Mechanisms for sticking include static electricity and film-to-film suction. In a system that relies only upon an input number of films in a case and a digitizer counting the number of digitizer feed commands, the double feed error can cause a misassociation of patient information with CAD system output. To prevent this misassociation, an operator may monitor the processing, stop the processing when a double feed is observed, reload the affected films, and re-start the processing. This is clearly an inefficient use operator time. Alternatively, the CAD system may detect the double feed error, and stop the batch processing. This has the undesirable effect of delaying the night's processing until the operator corrects the situation the following morning. Clearly it is desirable to provide a system and method for allowing automated handling of feed errors in a batch processing environment.